1. Field of the Invention
The invention relates to a tank ventilation system and to a method for tank ventilation.
2. Description of the Related Art
Motor vehicles conventionally have an activated carbon filter between the environment and the tank that supplies the internal combustion engine with combustible fuel. The activated carbon filter functions as a buffer for fuel vapors from the vapor chamber of the tank, and specifically from those regions of the tank that are not filled with fuel. The activated carbon filter is regenerated or purged on demand with a fresh air flow that is conducted over the hydrocarbon-laden carbon particles. The fresh air flow absorbs the hydrocarbons and transports the hydrocarbons to the internal combustion engine. The hydrocarbon-laden air flow from the activated carbon filter then is admixed to the combustion air and is burned with the combustion air.
The internal combustion engine is operated only intermittently in a hybrid vehicle or a vehicle with an automatic start/stop function. This intermittent operation of the internal combustion engine may cause some purging cycles to be omitted. There is a risk, therefore, that the activated carbon filter can no longer absorb the incoming hydrocarbon vapors and “overflows”. To prevent this, the tank internal pressure may be increased above the ambient pressure to reduce the quantity of hydrocarbon vapors generated in the tank and thus to reduce the supplied quantity of hydrocarbon vapors. Such an approach is known from the generic DE 40 40 895.
In view of the above situation, objects of the invention are to improve tank ventilation and to define an improved method for ventilating a tank.